High poly blade sculpted axe with Notches in it baked to low poly model with that has no notches in its mesh
No it isn't possible.

Baking a normal map only affects the shading of an object's surface to give the appearance of detail that would normally be created with extra geometry. A normal map cannot alter the outline of a mesh. You will need to have the notches in the outline of your low poly object.

While a displacement map can be used to move existing geometry, I don't expect it to fit into your usage. It would also mean having the geometry to displace.

Creating a transparency map would not get the result you are after. The material transparency can be restricted to certain areas but that area would be transparent from every angle, leaving the axe with a hole through it when looking towards the blade.